Conventionally, as a post-processing apparatus, connected to an image forming apparatus, for performing post-processing on plural print sheets printed with the image forming apparatus, a bookbinding machine which performs binding processing on a sheet bundle including printed text sheets with a book cover sheet to manufacture a book as a printed matter is widely used.
Further, as one bookbinding processing form in this type of bookbinding machine, so-called “case binding” of pasting a predetermined position (the back of the book) of a paper bundle of stacked plural sheets after image formation as text sheets, and covering up the pasted paper bundle with a cover sheet to attach the cover sheet to the paper bundle is known.
In the case binding, when pasting is performed in a state where the bundle of text sheets has curls and waviness, it is impossible to fully attaching the paste to the entire overlap part in the bundle of text sheets, and some text sheets may drop out of the cover sheet after the binding. Accordingly, an apparatus disclosed in Patent Literature 1 for performing bookbinding on a bundle of text sheets in an appropriate state is known.
A sheet bundle holding apparatus disclosed in Patent Literature 1 brings sheet-bundle posture correction members to correct curls and waviness of the sheet bundle into contact with an approximately central part of the sheet bundle while moving movable grip plates provided with the sheet bundle position correcting members. As a region where the sheet bundle position correcting members are in contact and pressed is gradually expanded outward by the approaching action of the movable grip plates with respect to the sheet bundle, it is possible to hold the sheet bundle while suppressing the curls and waviness.